Aircraft nacelles are intended to house a turboreactor, in particular a dual-flow turboreactor capable of generating a hot air flow (also called primary flow) coming from the combustion chamber of the turboreactor, and a cold air flow (secondary flow) coming from the fan that circulates outside the turboreactor through an annular channel, also called “jet,” formed between a fairing of the turboreactor and an inner wall of the nacelle. The exhaust section of the secondary flow is called “secondary jet nozzle,” while the exhaust of the primary flow is done in the primary jet nozzle. Behind the nacelle, the primary and secondary flows mix.
This nacelle is then generally equipped with a thrust reverser. The thrust reverser makes it possible, during landing of an airplane, to improve the braking capacity of the airplane by reorienting at least part of the thrust generated by the turboreactor forward. In this phase, the reverser obstructs the jet nozzle of the gases and orients the jet stream from the engine toward the front of the nacelle, thereby generating a counter-thrust added to the braking of the airplane's wheels.
In this perspective, the thrust reverser comprises varied thrust reversal means, such as in general at least one mobile cowl, called “thrust reverser cowls,” moving in translation owing to actuators in a direction substantially parallel to a longitudinal axis of the nacelle. Thus, the mobile cowl(s) can alternatingly go from a closed position, in which the thrust reverser cowl(s) ensure(s) the aerodynamic continuity of the nacelle, to an open position, in which a passage is exposed on a fixed structure of the nacelle to reverse the secondary flow.
Furthermore, an additional device can in particular make it possible to vary the section of the variable secondary jet nozzle. Although several embodiments exist, it is known to use a multitude of jet nozzle flaps able to pivot inside the jet as device so as to vary the width of said jet. In this way, it is possible to adapt the section of the secondary jet nozzle, so as to optimize the specific consumption of the turboreactor or reduce the exhaust noise from the gases depending on the flight phases.
One particular example is the embodiment described in patent Ser. No. 08/04295, where the jet nozzle flaps are situated at the outlet of the jet and also serve to vary the secondary jet nozzle during a limited translation of the thrust reversal cowl(s).
The jet nozzle flaps and the thrust reversal cowls constitute mobile panels. The displacement of such panels is ensured by a plurality of actuators.
The actuators can assume different forms, in particular electromechanical actuators like those described in document EP 0 843 089.
This type of actuator is associated with a control system comprising at least two motors able to drive said actuators. The control system is intended in particular to electrically power the motors and control the operation thereof.
The availability of the system for varying the secondary jet nozzle section is an important consideration and is a key area of the development of electromechanical actuators.
The availability criterion refers to the capacity of the means to be deployed so as to perform the function of adjusting the cycle of the turboreactor and avoid operating in a deteriorated mode. It requires a level of redundancy of the means, without, however, severely damaging the reliability of the entire device, and a suitable architecture for minimizing common modes, such as mechanical blocking.